Apparatus and methods for providing a package substrate and assembly for a flip chip integrated circuit. A substrate is provided having a solder mask layer, openings in the solder mask layer for conductive bump pads, and openings in the solder mask layer between the conductive bump pads exposing a dielectric layer underneath the solder mask layer. A flip chip integrated circuit is attached to the substrate using a thermal reflow to reflow conductive solder bumps on the integrated circuit to the conductive bump pads. An underfill material is dispensed beneath the integrated circuit and physically contacting the dielectric layer of the substrate. In additional embodiments, one or more integrated circuits are flip chip mounted to the substrate. The resulting assembly has improved thermal characteristics over the assemblies of the prior art.